Ferberite

Ferberite
Fluorapatite on ferberite from Minas da Panasqueira, Beira Baixa, Portugal
General
Category	Tungstate mineral
Formula (repeating unit)	FeWO4
Strunz classification	4.DB.30
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P2/c
Unit cell	a = 4.72, b = 5.7 c = 4.96 [Å]; β = 90°; Z = 2
Identification
Color	Black, dark brown in transmitted light
Crystal habit	Bladed crystals; massive
Twinning	Contact or interpenetrant or lamellar twins
Cleavage	Perfect on {010}; partings on {100} and {102}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	4–4.5
Luster	Submetallic to metallic adamantine
Streak	Brownish black
Diaphaneity	Nearly to entirely opaque
Specific gravity	7.58
Optical properties	Biaxial (+)
Refractive index	nα = 2.255 nβ = 2.305 nγ = 2.414
Birefringence	δ = 0.159
2V angle	Measured: 66°
Other characteristics	Slightly magnetic
References

Ferberite is the iron endmember of the manganese - iron wolframite solid solution series. The manganese endmember is hübnerite. Ferberite is a black monoclinic mineral composed of iron(II) tungstate, FeWO₄.

Ferberite and hübnerite often contain both divalent cations of iron and manganese, with wolframite as the intermediate species for which the solid solution series is named.

Ferberite occurs as granular masses and as slender prismatic crystals. It has a Mohs hardness of 4.5 and a specific gravity of 7.4 to 7.5. Ferberite typically occurs in pegmatites, granitic greisens, and high temperature hydrothermal deposits. It is a minor ore of tungsten.

Ferberite was discovered in 1863 in Sierra Almagrera, Spain, and named after the German mineralogist Moritz Rudolph Ferber (1805–1875).

Twinned Ferberite, Tazna Mine, Atocha-Quechisla District, Nor Chichas Province, Potosí Department, Bolivia. 4.8 x 4.0 x 3.6 cm.

Ferberite - Cínovec / Zinnwald, Erzgebirge; Krusné Hory Mts, Saxony & Ústí Region (Bohemia), Germany & Czech Republic